1. Field of the Invention
The present invention relates to an electroacoustical transducer assembly in general, and to a method and apparatus for mounting the vibratile diaphragm and the diaphragm tensioning spring in such a transducer, in particular.
2. Description of the Prior Art
Capacitance-type electroacoustical transducers are well known in the prior art. In such transducers, a diaphragm having an insulative layer and an electrically conductive surface has its insulative layer in contact with a grooved, irregular, electrically conductive surface of a substantially inflexible disc or backplate. The periphery of the diaphragm is maintained in a fixed position with respect to a transducer housing and a force from a spring member urges said backplate into tensioning engagement with said diaphragm. The insulative layer, the electrically conductive surface of said diaphragm constituting a first electrode, and the conductive surface of said backplate constituting a second electrode, form a capacitor such that when a dc bias voltage is applied across said electrodes, irregularities in said backplate surface set up localized concentrated electric fields in said insulative layer. When an ac signal is superimposed on said dc bias, the diaphragm is stressed such that oscillatory formations develop causing an acoustical wave front to be propagated from said diaphragm. A received acoustical wave front impinging on the diaphragm produces a variable voltage across said capacitor electrodes.
An extremely important design consideration for the above-described transducer is the amount of tension in the transducer diaphragm. In addition to such factors as resonant frequency and signal output magnitude, diaphragm tension also affects transducer sensitivity in at least two additional ways. Within limits, less diaphragm tension provides greater reception sensitivity. Also, excessive diaphragm tension may introduce stress patterns into the diaphragm which may affect the ability of the diaphragm to uniformly contact its associated backplate surface.
Prior art electroacoustical transducers have the periphery of their vibratile diaphragms clamped to a housing member or other such support structure after a predetermined amount of diaphragm tensioning force has been applied. A housing or support structure of this type necessarily increases the size of an electroacoustical transducer, primarily transducer diameter. Furthermore, as the overall size of a conventional capacitance-type transducer is reduced, the transducer housing or the structure that peripherally clamps the transducer diaphragm will consume a larger percentage of the overall transducer diameter. In addition to the increased cost of a physically larger transducer, additional space must be provided to contain the additional size, space that is often at a premium, especially in relatively light weight portable apparatus such as a photographic camera.